1. Field of the Invention
This invention relates to a method for controlling a tufting machine used for manufacturing a tufted carpet by tufting pile yarns on a ground fabric.
2. Description of the Prior Art
Generally speaking, when controlling a conventional tufting machine, the number of stitches in a unit length of a tufted carpet is visually counted, a yarn length required for forming piles in a unit length of the carpet is calculated from the yarn weight to have been consumed, and the surface of the tufted carpet is inspected to ensure that it exhibits the desired color pattern. These factors are controlled, if necessary, by changing pulleys driving a spiked roller for the ground fabric and yarn feed rollers for the yarn to be tufted, respectively, or by manually adjusting speed changers of the same. However, such operations are very complicated and need higher skills and experience, and fine adjustment corresponding to the color pattern is very difficult.
To eliminate the above-mentioned drawbacks the present inventor has provided, in U.S. Pat. No. 4,267,787, a method for controlling a tufting machine in which the stitch number and the yarn feed length for a unit supply length of the ground fabric are measured continuously on the machine and, if the measured value or values exceeds an allowable range of the standard value, the supply rate of the ground fabric or the yarn are automatically controlled. In the method disclosed in the above U.S. patent, the revolution of the spiked roller is not reliable as a base for measuring a supply length of the ground fabric because the spikes are not always stuck into the ground fabric to a constant depth but to various depths according to the thickness of the fabric. Further, the spiked roller is disposed in a region remote from a driving source of the machine and connected thereto through various power transmitting mechanisms, therefore motion of the roller tends to be inaccurate. As a result, the method in which the standard values are determined for a unit supply length of the ground fabric lacks stability and is unsuitable for precise control.
In the market, a price of the tufted carpet largely depends on the weight of the pile yarn to be used. A trading price is agreed with both the carpet maker and the buyer referring to the designed weight of the yarn upon ordering. Thus, if the yarn weight exceeds the expected amount in the actual carpet, the carpet maker suffers an economical setback. Accordingly, it is important for the carpet maker to control a yarn weight for a unit area, usually for one square meter, of the resultant carpet (hereafter referred merely to as "yarn weight"). In addition, the yarn weight is the product of a yarn length to be used for tufting a ground fabric along a 1 m length thereof, the number of yarns required to cover a 1 m width of the ground fabric, and a yarn thickness. In the past, the measurement of the yarn weight is carried out by cutting out a 1 m square swatch from the tufted carpet, pulling out the pile yarns from the swatch and weighing them with a scale. To prepare the swatch, a 1.5 m length end portion has to be separated from the adjacent portion of the finished carpet. This causes a considerable pile yarn loss as well as an undue consumption of labour and operation time.